CAN STEVIA LEAF EXTRACTS PROTECT BETA CELLS AGAINST GLUCO- OR LIPOTOXICITY?

In the present study, the effects of leaf extracts of two Stevia rebaudiana Bertoni biotypes (namely ST2 and ST3) on beta cells exposed to gluco- or lipotoxic conditions have been evaluated. Leaf extracts were obtained through innovative and eco-friendly extraction technologies, able to obtain enriched fractions of desired bioactive compounds. Leaf phytochemical composition was spectrophotometrically assessed, in terms of total phenols and flavonoids as well as for their anti-radical and anti-oxidant activity, evaluated by DPPH radical-scavenging assay and ferric reducing antioxidant power (FRAP), respectively. Furthermore, the content and profile of the main steviol glycosides was analysed by HPLC, using an HILIC column under isocratic conditions, and quantified through standard curves of pure standard mixtures. MTT assay was used in order to evaluate the protection effect of stevia leaf extracts on beta cells exposed to gluco- or lipotoxicity conditions. INS-1E cells were exposed for 4 days to 30 mM glucose or 24h to 0.5 mM palmitate with or without increasing concentrations of stevia leaf extracts.The phytochemical characterisation revealed that ST2 had higher total phenolic and flavonoid content and antioxidant activity, in comparison with ST3. Conversely, ST3 showed higher (p<0.05) concentration of stevioside than ST2. Chronic exposure to high glucose concentration reduced INS-1E cells viability (-40%), that was completely prevented by exposure to 50 or 200 μg/mL ST2 and partially, but significantly, in the presence of ST3 genotype. Similarly, 24h exposure to palmitate resulted in a decrease of INS-1E viability (-20%), that was counteracted by both ST2 and ST3. The study shows that Stevia rebaudiana extracts have beneficial effects on viability of beta cells exposed to gluco- or lipotoxic conditions, possibly depending on their phytochemical composition and related antioxidant capacity.